Biochemical aspects of GI disease and nutrition Flashcards
During a clinical assessment what is normal for the patient in terms of nutrition?
weight - loss or gain (intentional or unintentional)
food intake
chewing/swallowing
GI symptoms - nausea, vomiting, altered bowel habits
drugs/alcohol
How can you assess food intake?
dietary recall
food diaries - unweighed food record
food weighing
What functional assessments can be done to assess nutritional status?
muscle mass - grip strength / isometric knee extension / response to electrical stimulation
hepatic secretory proteins - albumin (<35) and transferrin (<1.5g/L)
immune response in malnourished patients - cell mediated immunity
How is malabsorption defined?
wide group of conditions associated with disordered biochemistry
no specific clinical presentation - may be a group of signs or symptoms
What is the prevalence of undernutrition in hospital?
40%
What are the effects of malnutrition?
Impaired immune response - infection
decreased respiratory muscle strength - increased incidence of chest infection
impaired wound healing - prolonged recovery
inactivity - thromboembolism, pressure sores
decreased skeletal muscle strength - fatigue, inactivity, falls
impaired thermoregulation - hypothermia
How does malabsorption present and why?
pale bulky (offensive) stools - fat malabsorption or digestion abdominal distention, watery diarrhoea, and xs flatus - malabsorption of carbohydrate vague malaise, tiredness and weight loss - generalised deficiency of nutrients anaemia - deficiency of iron folate or B12 easy bruising or bleeding - deficiency of vit K failure to thrive - generalised deficiency of nutrients
How can you estimate nutritional requirements?
energy requirements = calorimetry
estimation from body weight = 25-35 kcal/kg/24 hours
prediction equations = schofield equation, harris-benedict equation and ireton-jones formula
How is basal metabolic rate calculated?
Male
BMR = 66.5 +13.75Weight +(5height-6.77age)
Female
BMR = 66.5 +19.56Weight +(1.85height-4.67age)
How does BMR vary between age and height?
With increasing height your BMR increases and with increasing age your BMR reduces
What are the different types of sugars?
intrinsic = naturally e.g. as part of the cellular structure
extrinsic = non-natural e.g. refined sugars
What are the different types of starches?
alpha glucan polysaccharides
Amylose= straight chain glucose polymer with molecular mass 100,000Da
Amylopectin = branched chain glucose polymer with molecular mass >100,000
How are carbohydrates chemically digested?
salivary amylase, pancreatic amylase and brush border enzymes (dextrinase, glucoamylase, lactase, maltase and sucrase)
How are carbohydrates absorbed?
secondary active transport (cotransport) with Na
Facilitated diffusion of some monosaccharides = enter the capillary beds in the villi, transported to the liver via the hepatic portal vein
Where is amylase found and what does it produce?
salivary and pancreatic
- digestion of alpha1,4- bonds in starch
= produces = maltose, maltotriose, short branched oligosaccharides and alpha-limit dextrins
How does maltase work and what does it produce?
splits glucose from alpha-1,4 bonds in starch up to 9 residues long
producing glucose
How does sucrase work and what does it produce?
splits sucrose producing glucose and fructose
How does isomaltase work and what does it produce?
splits glucose monomers from non-reducing ends of alpha limit dextrins
producing glucose
How does lactase work and what does it produce?
splits lactose producing galactose and glucose
How much of dietary starch isn’t absorbed?
up to 20%
- carbohydrates in the bowel are metabolised by bacteria to produce short chain fatty acids (energy source for colonocytes) + methane + hydrogen
What are primary and secondary lactase deficiencies?
primary = eu 5-15%, africans/asians >70%
secondary = IBD, chronic alcoholism, coeliac disease, tropical sprue
How can you investigate for carbohydrate absorption?
xylose absorption
- pentose sugar 50% excreted in urine - not reliable test so not used
lactose intolerance test
- serial glucose measurements after 50g lactose
hydrogen breath tests
- glucose hydrogen breath test = bacterial overgrowth in the small intestine
- lactose hydrogen breath test = problem digesting lactose
- fructose hydrogen breath test = difficulty digesting fructose
- sorbitol hydrogen breath test = sorbitol is a sugar alcohol used to to investigate rapid intestinal transit
- lactulose hydrogen breath test = galactose and fructose transported intact to the colon measure of ororectal transit time
How is fat absorbed?
emulsified by bile phospholipids
stabilised by bile salts
lipase digestion to monoacylglycerol and free fatty acids
solubilised in micelles
What are the stages of fat digestion and absorption?
1) pre-treatment = emulsification by bile salts
2) enzymes - pancreatic lipase
3) absorption of glycerol and short chain fatty acids = absorbed into capillary blood villi and transported via hepatic portal vein
How are monoglycerides and fatty acids absorbed?
cluster with bile salts and lecithin to form micelles
then released by micelles to diffuse into epithelial cells
then combine with proteins to form chylomicrons
then enter lacteals and are transported to systemic circulation
What are essential fatty acids?
phospholipids - linoleic acid and alpha- linoleic acid
precursors of arachadonic acid, eicosapenaenoic acid and docosahexaenoic acid
What is fat absorption dependent upon?
bile production - dependent on liver secretion = bile salts, phospholipids and cholesterol and also having patent ducts
pancreatic enzymes = functional lipase
How can fat absorption be investigated?
faecal fat excretion
- 3/5 day collection
- usual diet pre-collection
- outmoded, no longer used
14C-triolein breath test
- if 14C labelled triolein absorbed, 14C02 will appear in breath
- but lung/liver disease may give false results
How are proteins digested and absorbed?
pepsin in stomach
pancreatic proteases = trypsin, chymotrypsin and carboxypeptidase
brush border enzymes = aminopeptidases, carboxypeptidases and dipeptidases
absorption of amino acids is coupled to active transport of Na
How can protein metabolism be measured?
nitrogen balance
- pts on ITU or long term nutrition
- nitrogen excretion = urinary nitrogen + faecal nitrogen
- variability of faecal output
What is urinary nitrogen made up of?
urinary urea nitrogen and non-urea nitrogen (20%)
- urinary urea nitrogen can be used as an assessment tool but is less useful with increasing severity of illness and inaccurate where there is urine infection
What is faecal pancreatic elastase 1?
elastase is a protein cleaving enzyme produced by the pancreas
resistant to degradation by other enzymes and is excreted into the gut therefore it can be measured in the stool
- enzyme is reduced in pancreatic insufficiency
What is serum immunoreactive trypsin (IRT)?
assessing pancreatic function
- increased IRT indicates obstruction
- used as a screening test for CF in new born babies
- low serum values indicate failure of production in pancreatic disease
Where are vitamins absorbed?
small intestine
- fat soluble = A, D, E and K - carried by micelles and then diffuse into absorptive cells
- water soluble vitamins= B and C are absorbed by diffusion or by passive or active transporters
- vit b12 binds to intrinsic factor and is absorbed by endocytosis
What vitamins are absorbed in the large intestine?
K and B from bacterial metabolism
What are some sources of vitamin A ?
preformed vit A = retinol
- liver, fish oils, diary
Carotenoid pigments - beta-carotene
- carrots, dark green leafy veg
What happens if you have vit A deficiency?
night blindness
What happens if you have an excess of vit A?
Acute
- raised ICP, nausea, vomiting, visual disturbances
chronic
- liver/bone damage+/- teratogeneicity
What are the sources of vit E?
8 similar compounds - intake is proportional to intake of polyunsaturated fatty acids
- tocopherols = alpha is the most abundant
present in cell membranes - antioxidant
What happens if you have a deficiency of vit E?
premature infants= haemolytic anaemia and thrombocytopenia
Children/young adults spinocerebellar degeneration
parenteral nutrition
What happens if you have an excess of vit E?
relatively non-toxic
What are sources of thiamine / vitamin B1?
wheat germ, oatmeal and yeast
What happens if you are deficient in thiamine?
beriberi
- dry = peripheral neuropathy, muscle weakness, fatigue
- wet = oedema and heart failure
common in 1st world as wernickes encephalopathy
How is a thiamine deficiency assessment carried out?
direct measurement of thiamine before giving any
- previously erythrocyte transketolase measurement - not used for assessment
What happens if you have an excess of thiamine?
non- toxic
not recognised as a problem
What are some sources of riboflavin / vitamin B2?
flavoproteins = flavin mononucleotide, flavin adenine dinucleotide = electron carrier in biological oxido-reduction systems
sources = eggs, green veg, milk and meat
What happens if you have a deficiency of riboflavin?
angular stomatitis, painful red tongue with sore throat
oily scaly skin rashes
eye sensitive to light
anaemia
birth defects including congenital heart defects and limb deformities
How is a riboflavin deficiency assessed?
urinary excretion (poor measure) red cell glutathione reductase (very limited use)
What are some sources of nicotinamide/vitamin B3?
yeast, meat, milk and green veg
What does a deficiency in nicotinamide/b3 cause?
pellagra = rare in developed world usually secondary to alcoholism, long term diarrhoea
replacement is non-toxic
What are some sources of vitamin B6?
pyridoxal, pyridoxine, pyridoxamine + 5-phosphates
= fortified breakfast cereals, meat, bananas, chickpeas, potatoes, pistachios
What does a deficiency in vitamin B6 cause?
seborrhoeic dermaitis, atrophic glossitis, neurologic symptoms of somnolence, confusion, neuropathy and sideroblastic anaemia
What is zinc an essential component of and what does a deficiency cause?
essential for over 200 enzymes
- deficiency = inadequate intake (parenteral feeding) and increased loss (diarrhoea)
How can you assess zinc levels?
plasma zinc
urinary zinc
used in pts on parenteral nutrition
What can an excess of copper cause?
difficult to cause an excess
Wilson’s disease
- assess by looking at plasma and urine copper and caeruloplasmin
What is selenium important for and what happens with deficiency and excess?
essential co-factor of glutathione peroxidase
deficiency = parental nutrition
excess - animals, poisoning
What are the key ways of supplementing nutrition?
food supplements
enteral (using gut)
parenteral (using IV)
What is enteral feeding?
nutrients delivered to the gut - stimulate gut hormones - helps maintain gut integrity - nutrients absorbed into portal circulation - more physiological than TPN there are different routes of delivery
What are the indications for enteral nutrition?
disturbed swallowing e.g.MND
upper GI obstruction e.f. oesophageal stricture
Inability to eat e.g. head injury, critical illness
GI disease e.g. pancreatic insufficiency
High requirements e.g. burns, trauma
Loss of appetite e.g. anorexia nervosa, cardiac cachexia
What are the sources of delivery of enteral feeds?
into the stomach
- nasogastric or orogastric tube
- gastrostomy
- oesophagostomy
beyond stomach
- nasoduodenal tube
- jejunostomy
How does TPN work?
via circulation therefore bypassess GIT and liver (1st pass metabolism)
3 chamber inner bag - glucose, amino acids and fat emulsion separately
- oxygen absorber and then overpouch (light sensitive)
- intralipid can cause fever, shivering, chills and N+V but rare
What are the indications for TPN?
Lack of functioning GIT “intestinal failure”
- blockage
- reduced absorptive capability
- temporary or permanent
the oral/enteral route will not maintain adequate nutrition - eg. premature infant
needs to rest GIT
- gastroschisis prolonged diarrhoea
- high output fistulae
- anastomosis
What are some causes of hypokalaemia?
insufficient for excessive losses/depletion
e.g. D+V, renal or anabolic phase i.e. refeeding, insulin or alkalosis
What are some causes of hyperkalaemia?
renal failure, increase catabolism and cell breakdown, acidosis
What are the causes of hyponatraemia?
pseudo due to lipaemia
increased ADH release and poor regulation of fluid balance
water overload/ Na loss
rarely high loss e.g. fistula, drain, renal
need low Na and H20 feed if hypo seconadry to ascites / oedema
What are some causes of metabolic bone disease?
steroid use, SBS, inactivity, menopause
What is refeeding syndrome?
consisting of metabolic disturbances that occur as a result of reinstitution of nutrition to patients who are starved, severly malnourished or metabolically stressed due to severe illness
when too much food and/or liquid nutrition supplement is consumed during initial 4-7 days of re-feeding => synthesis of glycogen, fat and protein in cells, to the detriment of serum conc of K, Mg and phosphorus
the low serum minerals, if severe enough can be fatal
What patients are at risk of re-feeding syndrome?
pts with anorexia nervosa pts with chronic alcoholism oncology pts postoperative pts elderly patients uncontrolled DM chronic malnutrition long term use of antacids long term use of diuretics
What is calprotectin a sign for ?
used to investigate the cause persistent watery or blood diarrhoea
can be requested with stool culture to detect bacterial infection
-useful to determine if IBD or IBS
What is faecal immunohistochemical test?
type of faecal occult blood test - uses antibodies that specifically recognise human hb
- used to detect and quantify the amount of blood in a single stool sample
